NGT_Padre

I have this problem. No mater what I do it still appears, not on every stl file but often. I already tried making walls thicker or looking for some hidden option that i have enabled without me knowing. Photos show unsliced model (without horizontal spaces) and sliced (with horizontal spaces). I go back to school in 2 days and I don't wanna waste my free time on solving these kinds of issues so I gave up and signed up to make this topic. Please help.